Problem with displaying float value

[mirluk]

Hi,
I'm trying to display float value on the screen (temperature, 27,2 °C for example) but I'm getting just integer value (27,0°C).

Part of temperatue.cpp:

void Temperature::setValue(int value)
{
	this->value=value;
	update();
}
 
 
void Temperature::paint(QPainter* painter)
{
...
	float x = (((((value)-6400)*120)/25600)-40);
	digitalValue = QString("%1").arg(x,0,'f',1);
	painter->drawText(0,0, 40,20, Qt::AlignRight, digitalValue);
...
}

void Temperature::setValue(int value)
{
	this->value=value;
	update();
}


void Temperature::paint(QPainter* painter)
{
...
	float x = (((((value)-6400)*120)/25600)-40);
	digitalValue = QString("%1").arg(x,0,'f',1);
	painter->drawText(0,0, 40,20, Qt::AlignRight, digitalValue);
...
}

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[mcosta]

The problem is here

float x = (((((value)-6400)*120)/25600)-40);

float x = (((((value)-6400)*120)/25600)-40);

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All factors are integers, then the result is an integere value converted to float. Try this

float x = (((((value)-6400)*120.0)/25600)-40);

float x = (((((value)-6400)*120.0)/25600)-40);

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or

float x = ((((static_cast<float>(value)-6400)*120)/25600)-40);

float x = ((((static_cast<float>(value)-6400)*120)/25600)-40);

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[sebastian]

Hi,

I think that "setValue()" should take float instead of int argument.
Otherwise value which you're passing will always be converted to int.

Btw. line:

float x = (((((value)-6400)*120)/25600)-40);

float x = (((((value)-6400)*120)/25600)-40);

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for "value"(s) such that:

fabs(value-6400) < 25600/120

fabs(value-6400) < 25600/120

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will always give you -40. But maybe that's what you want...

[mirluk]

Ok, I solved it on my own way.

Now, the code looks:

void Temperatura::setValue(float value)
{
	this->value=value;
	update();
}
 
 
void Temperatura::paint(QPainter* painter)
{
...
	float x = (float)(((value-6400)*120)/25600)-40.0;
	digitalValue = QString("%1").arg(x,0,'f',1);
	painter->drawText(0,0, 40,20, Qt::AlignRight, digitalValue);
...
}

void Temperatura::setValue(float value)
{
	this->value=value;
	update();
}


void Temperatura::paint(QPainter* painter)
{
...
	float x = (float)(((value-6400)*120)/25600)-40.0;
	digitalValue = QString("%1").arg(x,0,'f',1);
	painter->drawText(0,0, 40,20, Qt::AlignRight, digitalValue);
...
}

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Anyway, thanks mcosta and sebastian for answers.